I have a Warwick RockBass Corvette $$ that has a few loose knobs. the pots do not seem to be loose at all and do not move it is only the knobs. I do not know how to tighten these knobs as there are no screws visible on the knob. I tried removing the knob by pulling it off thinking they must be pull off knobs but I am afraid to pull any harder than I already have. Can anyone help me get these knobs to stop wiggling around?